NORTHAMPTON — Emergency repairs on a bridge on the northbound side of Interstate 91, which snarled traffic all day, have been completed earlier than expected, officials said.

Although state Department of Transportation spokesman Michael Verseckes initially projected a 4 p.m. reopening of the left-hand lane, he said workers were able to complete the repair by 2 p.m.

“They just finished,” Verseckes said. “They wrapped it up earlier than expected.”

Lt. Daniel Richard, a spokesman for state police, said all lanes are now open. However, the backed-up traffic will likely take some time to dissipate.

The emergency work began about 6 a.m., and state police reported that northbound traffic backed up for miles as the morning commute got underway. Traffic, state police said, backed up as far as Exit 17 in Holyoke and beyond.

The bridge in question spans Island Road. Repairs were required on the joint where the bridge deck meets the bridge abutment in the left shoulder and left travel lane, Verseckes said.

At least one accident, believed to have been caused by an inattentive motorist crashing into slow-moving vehicles ahead, was reported, Sgt. Adam Hakkarainen said. Troopers also were busy with motorists attempting to back their way down on-ramps to get out of the mess or doing U-turns on the interstate, Hakkarainen said.